McPhee is responsible for a respectable pile of books all dedicated to converting the ignorant into enthusiasts. Here he offers us a book on geology. To research his subject, he traveled with one geologist or another across the country on Route I-80, learning to read the autobiography of the earth written in the rocks. Wherever road builders have sliced through the rock, the reading becomes easy.McPhee wants us to grasp the concept of a million years and to free ourselves of the conventional boundaries of human time, and he accomplishes this purpose by using dramatic fact, poetry, and humor. The reader who perseveres through the generous sprinkling of technical jargon is amply rewarded.